1. Field of the Invention
This invention relates to dental compositions, and more particularly, to dental compositions useful as a primer or an adhesive to be applied to the surface of teeth and/or dental materials to thereby effect adhesion.
2. Description of the Background Art
Solutions of liquid methacrylate monomer and an organic peroxide, such as dibenzoyl peroxide, in a volatile organic solvent, are used in dentistry in adhesives or primers. The problem with these solutions is that they tend to undergo polymerization in storage. Therefore, such solutions are usually kept in containers characterized by high oxygen permeability, such as polyethylene or polypropylene. They are also kept in rather small containers, usually of a volume as small as about 10 cc, to facilitate a constant supply of oxygen gas to the solvents, which prevents the solution from polymerizing. The typical volatile organic solvents used in those solutions such as hydrocarbons, esters and ketones have a relatively low molecular weight and therefore permeate readily through plastics of high oxygen permeability. Therefore, when a solution of a methacrylate monomer diluted with such organic solvent is kept in a plastic container, the organic solvent permeates through the container, resulting in a volume reduction of the solution.
Alcohols, such as ethyl alcohol and isopropyl alcohol are known diluting solvent for dental priming agents or dental adhesives. Although such alcohols do not permeate through the above plastics, they have the drawback that they accelerate the decomposition of the organic peroxides. Compositions of free radical-polymerizable monomers, an organic peroxide, and alcohol, therefore are rapidly reduced in content of organic peroxide, or they tend to solidify due to polymerization. Hence, it has been impossible to store such solutions for extended periods of time. Accordingly, it has been difficult to provide dentists with primers or adhesives of stable compositions of a free radical-polymerizable monomer, organic peroxide, and volatile solvent.